Dressing materials for application to the surface of wounds should desirably be nonadherent to the moist wound surface, but sufficiently tacky to allow attachment of the dressing to intact skin around the wound and attachment to further dressing layers such as absorbent layers. For this purpose a soft or tacky hydrophobic material is suitable for the material. The wound contacting material should desirably be liquid-permeable to allow passage of wound fluid, especially for heavily exuding wounds such as burns. The material should also be non-irritating, inexpensive, and stable to common sterilization methods such as ionizing radiation.
Traditional tulle gras dressings generally consist of a layer of gauze coated with paraffin wax. Such dressings have a number of desirable properties, and for this reason have been used extensively for many years. Among these advantages are their high degree of conformability and deformability, and the fact that their tackiness makes them very easy to apply. That is to say, a tulle gras dressing applied to a wound will usually remain in place simply by adhesion of the paraffin wax to the patient's skin (or to itself in the case of a dressing wrapped around a finger, for example) while a securing bandage is applied. Tulle gras dressings are also quite inexpensive. However, tulle gras dressings do have a number of disadvantages. Principal amongst these is that, although initially nonadherent, they often become “dry” (in the sense of losing their paraffin coating) and consequently adhere to the wound to which they are applied. This effect is due to the paraffin coating becoming mobile at body temperatures and migrating into the wound or being absorbed into the backing of the dressing or bandage. In some cases, removal of a tulle gras dressing which has become dry in this way can cause considerable trauma. Indeed, it is quite common to have to soak tulle gras dressings in order to remove them. If tulle gras dressings are changed more frequently, in an attempt to avoid them becoming attached to the wound, this may delay wound healing and adds to nursing costs.
A further disadvantage of traditional tulle gras dressings is that fibres from the gauze may become incorporated in the wound, as may the paraffin coating of the dressing. Some authorities see the migration of paraffin into a wound as an undesirable effect and any paraffin found in a wound can be difficult to remove with normal aqueous wound cleansing agents. Moreover, the pores of the gauze may become occluded if the paraffin coating is too heavy or as a result of the mobility of the paraffin during use of the dressing. While occlusive dressings are appropriate in some circumstances, it is undesirable that the nursing staff should have no control over whether the dressing used is in fact occlusive.
Still further disadvantages of conventional tulle gras dressings are that they are effectively opaque and of somewhat unsightly appearance, and the paraffin can run during storage, making them particularly messy to apply.
EP-A-0251810 describes wound dressing materials that overcome the above disadvantages by replacing the paraffin wax coating of conventional tulle gras by a tacky or non-tacky, hydrophobic silicone coating on a gauze or mesh substrate. In certain embodiments, the gauze may be provided with a tacky silicone coating on one side and a non-tacky silicone coating having a different composition on the other side. Similar materials are described in WO-A-8705206.
EP-A-0342950 describes similar wound dressings having a non-adherent silicone coating. The adherence of the silicone is reduced by addition of an amine-extended polyurethane.